Conventionally, a structure including an oil seal securing portion for securing an oil seal attached to a crankshaft is known. Such a structure is disclosed in JP2000-46196A, for example.
In JP2000-46196A, an oil seal come-off prevention apparatus, which includes an oil seal attached to a rotational shaft (a crankshaft), a housing including an opening at which the oil seal attached to the rotational shaft is secured, and a lock ring fitted in an annular groove formed at an inner circumferential surface of the opening and thereby restricting the oil seal from falling off, is disclosed.